15 ECT Circuit - Temperature Out of Range Low

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The coolant temperature sensor (CTS) is a thermistor located in a coolant passage. When coolant temperature is cold the sensor has a high resistance, as temperature increases the resistance of the sensor decreases. The PCM provides a five volt signal to the coolant sensor, which is also connected to PCM ground. The PCM reads the voltage drop on the signal line to determine coolant temperature.

Code Parameters

Code 15 will set if:

  • The CTS reads below -35°C (-31°F).
  • The engine has been running longer than five minutes with a temperature less than -35°C (-31°F).

Diagnostic Aids

  • Refer to Temperature vs. Resistance Chart.
  • When attempting to diagnose an intermittent problem, use the Scan Tool to review supplemental diagnostic information.
    • The supplemental data can be used to duplicate a problem. Select MALF History from Scan Tool EC menu.
  • Check the tightness of the female terminal grip with a spare male terminal.
  • Start engine and observe CTS reading on Scan Tool.
  • Normal operation is for the CTS to rise smoothly to approx. 88°C (190°F) (thermostat opens) then stabilize.
  • Visually inspect CTS wires for damage. Wiggle wires while observing scan tool CTS reading and watch for a sudden shift in temperature.
  • CTS may be compared to ATS temperature, with a Scan Tool if engine has cooled overnight at ambient temperature. They should be within four degrees of each other with ignition On - engine Off

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